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115 lines
3.6 KiB
115 lines
3.6 KiB
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<title>Tremor - function - ov_read</title>
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<link rel=stylesheet href="style.css" type="text/css">
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<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
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<table border=0 width=100%>
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<tr>
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<td><p class=tiny>Tremor documentation</p></td>
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<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
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</tr>
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</table>
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<h1>ov_read()</h1>
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<p><i>declared in "ivorbisfile.h";</i></p>
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<p>
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This is the main function used to decode a Vorbis file within a
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loop. It returns up to the specified number of bytes of decoded audio
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in host-endian, signed 16 bit PCM format. If the audio is
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multichannel, the channels are interleaved in the output buffer.
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If the passed in buffer is large, <tt>ov_read()</tt> will not fill
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it; the passed in buffer size is treated as a <em>limit</em> and
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not a request.
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<p>
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Note that up to this point, the Tremor API could more or less hide the
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multiple logical bitstream nature of chaining from the toplevel
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application if the toplevel application didn't particularly care.
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However, when reading audio back, the application must be aware
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that multiple bitstream sections do not necessarily use the same
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number of channels or sampling rate. <p> <tt>ov_read()</tt> passes
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back the index of the sequential logical bitstream currently being
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decoded (in <tt>*bitstream</tt>) along with the PCM data in order
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that the toplevel application can handle channel and/or sample
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rate changes. This number will be incremented at chaining
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boundaries even for non-seekable streams. For seekable streams, it
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represents the actual chaining index within the physical bitstream.
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<p>
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<br><br>
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<table border=0 color=black cellspacing=0 cellpadding=7>
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<tr bgcolor=#cccccc>
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<td>
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<pre><b>
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long ov_read(<a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *buffer, int length, int *bitstream);
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</b></pre>
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</td>
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</tr>
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</table>
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<h3>Parameters</h3>
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<dl>
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<dt><i>vf</i></dt>
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<dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec
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functions.</dd>
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<dt><i>buffer</i></dt>
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<dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd>
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<dt><i>length</i></dt>
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<dd>Number of bytes to be read into the buffer. Should be the same size as the buffer. A typical value is 4096.</dd>
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<dt><i>bitstream</i></dt>
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<dd>A pointer to the number of the current logical bitstream.</dd>
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</dl>
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<h3>Return Values</h3>
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<blockquote>
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<dl>
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<dt>OV_HOLE</dt>
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<dd>indicates there was an interruption in the data.
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<br>(one of: garbage between pages, loss of sync followed by
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recapture, or a corrupt page)</dd>
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<dt>OV_EBADLINK</dt>
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<dd>indicates that an invalid stream section was supplied to
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libvorbisidec, or the requested link is corrupt.</dd>
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<dt>0</dt>
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<dd>indicates EOF</dd>
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<dt><i>n</i></dt>
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<dd>indicates actual number of bytes read. <tt>ov_read()</tt> will
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decode at most one vorbis packet per invocation, so the value
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returned will generally be less than <tt>length</tt>.
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</dl>
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</blockquote>
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<h3>Notes</h3>
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<p><b>Typical usage:</b>
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<blockquote>
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<tt>bytes_read = ov_read(&vf,
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buffer, 4096,&current_section)</tt>
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</blockquote>
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This reads up to 4096 bytes into a buffer, with signed 16-bit
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little-endian samples.
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</p>
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<br><br>
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<hr noshade>
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<table border=0 width=100%>
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<tr valign=top>
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<td><p class=tiny>copyright © 2002 Xiph.org</p></td>
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<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
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</tr><tr>
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<td><p class=tiny>Tremor documentation</p></td>
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<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
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</tr>
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</table>
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</body>
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</html>
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